Connecting rod-bearing combination for adjusting and reducing oscillating masses of a connecting rod-piston-combination and method for producing a connecting rod-bearing combination of this type

ABSTRACT

The invention relates to a connecting rod-bearing combination comprising a bearing for a small connecting rod eye of a connecting rod which serves to receive a piston pin that supports a piston. The invention also relates to a method for producing a connecting rod-bearing combination of the aforementioned type. The aim of the invention is to be able to exert an influence on the connecting rod-piston combination whereby enabling a fine tuning of the oscillating masses. To this end, the invention provides a connecting rod-bearing combination, which is post-machined in the area of the small connecting rod eye during which material is removed form a mass that corresponds to the difference between the oscillating mass of the connecting rod-bearing combination and a stipulated oscillating mass. The method for producing the connecting rod-piston combination is characterized in that during the removal of material, it is determined how much material mass on the connecting rod-bearing combination is to be removed in order to obtain a stipulated connecting rod-piston combination of a specified mass and mass distribution. The connecting rod-bearing combination is subsequently post-machined in the area of the small connecting rod eye during which material is removed to the extent of the determined mass.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to a connecting rod/bearing combination having abearing (1) for a small connecting rod eye (6) of a connecting rod (5),which serves to accommodate a piston pin mounting a piston and a methodof producing such a connecting rod/bearing combination.

2. Related Art

The background of the invention is the problem of the mass forcesarising in a driving mechanism. In the context of the present invention,a driving mechanism should be understood to mean the system consistingof piston, connecting rod and crankshaft, as used for example as a crankmechanism in internal combustion engines.

Irregular movements of masses, i.e. accelerated and deceleratedmovements, involve mass or inertial forces. The piston of an internalcombustion engine moves substantially in a straight line in thedirection of the axis of the cylinder liner and effects an oscillatingmovement. In the process, it is exposed to constantly varyingaccelerations, which reach their maximum at the reversal points of thepiston movement, the top and bottom dead centers. Corresponding to therectilinear movement of the piston, the accelerations and with them theinertial forces are directed in the direction of the cylinder lineraxis.

In contrast to the piston, the crank effects not an oscillating but arotating movement. The inertial forces acting thereon are thecentrifugal forces produced during rotary motion by the constant changein direction.

The most complex movement of the three components forming the crankmechanism is performed by the connecting rod. Movement of the connectingrod is a composite movement and comprises components of both oscillatingand rotary motion.

FIG. 1 is a schematic representation of a driving mechanism (20) havinga piston (21), a connecting rod (22) and a crank (23). A counterweight(26) is shown in dash-dotted lines.

FIG. 2 shows an equivalent system for the driving mechanism (20) shownin FIG. 1, wherein the equivalent system is composed of two point masses(24, 25), of which one sub-mass m_(h) (24) is arranged in the piston pincenter and performs oscillating motion and one sub-mass m_(r) (25) isarranged in the center of the cranked portion (23) of the shaft andeffects rotary motion with the crankshaft.

The background to this equivalent system is that the connecting rod massm_(P) may be broken down relative to the mass action of the connectingrod into an oscillating mass m_(ph) and a rotating mass m_(Pr). Theseequivalent masses are conventionally determined according to thefollowing equations:m _(P) =m _(Pr) +m _(Ph)m _(Pr)×1₁ =m _(Ph)×1₂,wherein 1₁, 1₂ indicate the spacing of the center of gravity of theconnecting rod from the equivalent point masses.

The oscillating equivalent mass m_(h) (24) is obtained from the sum ofthe piston mass m_(K) and the oscillating connecting rod mass m_(Ph).Accordingly, the rotating equivalent mass m_(r) (25) is obtained fromthe sum of the rotating connecting rod equivalent mass m_(Pr) and theshaft cranked portion mass m_(Kur) reduced to the crank radius r, whichis calculated as:m _(Kur) =m _(Ku) r ₁ /r

Here, r₁ is the spacing of the center of gravity of the cranked portion(23) of the shaft from the axis of rotation of the crankshaft, m_(Ku) isthe mass of the cranked portion of the shaft and r is the crank radius.

The mass forces, which are produced by the rotating mass m_(r) (25), maybe simply counterbalanced by an opposing counterweight (26). On theother hand, minimization or compensation of the inertial forces producedby the oscillating mass m_(h) (24) is problematic.

In general, research and development work is aimed at reducing themasses of all oscillatingly moved parts, in particular the piston, sincecompensation of the mass forces produced thereby cannot be handled bythe arrangement of counterweights. On the one hand, redesign of thereciprocating components using the smallest possible amount of materialis necessary, while on the other hand the use of new materials of lowerrelative density will also achieve the objective.

However, this procedure is also subject to limitations due to strengthrequirements, such that it becomes ever more difficult to minimize theoscillating masses and the mass inertial forces caused thereby.

In the case of multi-cylinder engines, it is possible to influence themass forces or the effect thereof by the number of cylinders, thecylinder arrangement, the crank sequence of the crankshaft and/or theignition sequence.

If, for example, in the case of a multi-cylinder engine, it is intendedto compensate the mass forces by means of a cylinder arrangementselected for this reason, this ideally requires the same drivingmechanisms for all the cylinders, comprising the same weight or the sameweight distribution. It is thus ensured that the driving mechanisms usedin one and the same engine produce uniformly large mass forces,especially uniformly large oscillating or rotary mass forces.

For manufacturing reasons, the components used do not exhibit exactlythe desired weight or the desired weight distribution, and thus nor dothe driving mechanisms composed thereof.

The prior art has attempted to compensate the deviation, caused bymanufacture, of the individual components with regard to mass and massdistribution as follows:

-   -   connecting rod and piston are subjected in each case        individually to a selection process, in which they are divided        into a large number of weight categories, and    -   connecting rod and piston are then grouped, with the objective        of achieving similar connecting rod/piston combinations,    -   wherein the connecting rod comprises counterweights both at the        connecting rod eye and at the connecting rod head, which are        machined to achieve exact adjustment of the mass or mass        distribution of the connecting rod/piston combinations.

In the process, it is necessary to take into account the fact that thecounterweights which are provided at the connecting rod eye and at theconnecting rod head and are also known as cams increase the total weightof the connecting rod and thus the total weight of the drivingmechanism. This means that merely providing these counterweights for thepurpose of adjusting the mass or mass distribution increases the weightand is thus inconsistent with the real objective of minimizing themasses of all the moving components.

For this reason, the attempt has been made to provide high-precisionmanufacturing methods with which low tolerances may be achieved. Byreducing or decreasing the manufacturing tolerances, the differencesbetween the components of a particular type are reduced at the sametime, such that the size of the counterweights to be provided maylikewise be reduced.

Production of the connecting rod with lower mass or mass distributiontolerances has been made possible by more recent methods, such that thenumber of weight categories necessary for selection has been greatlyreduced and, in the case of maximally optimized processes, onlyconnecting rods of one weight class remain.

When grouping these connecting rods with the associated pistons to forma connecting rod/piston combination, compensation of the connecting rodmass tolerances is effected by the piston. Nevertheless, there is arequirement for precision fine-tuning of the oscillating masses.

SUMMARY OF THE INVENTION

Against this background, it is the object of the invention to provide apossible way of influencing the connecting rod/piston combination bymeans of which fine-tuning of the above-mentioned type may be performed.

This object is achieved by a connecting rod/bearing combination in whichthe connecting rod/bearing combination is post-machined in the area ofthe small connecting rod eye in such a way that material is removed of amass which corresponds to the difference between the oscillating mass ofthe connecting rod/piston combination and a predetermined oscillatingmass.

In advantageous embodiments of the connecting rod/bearing combination,the bearing is a bushing provided in the small connecting rod eye. Ifmaterial is removed incorrectly, especially if too much material isremoved, the shortcoming may be readily remedied by replacing thebushing, whilst the connecting rod may continue to be used.

In advantageous embodiments of the connecting rod/bearing combination,the bearing is a plain bearing coating applied to the small connectingrod eye. When the material is removed, the bearing cannot slip, forexample rotate in the manner of a bushing.

The bearing, i.e. the bushing or the plain bearing coating, is arrangedin the connecting rod eye of the connecting rod and serves as bearingarrangement for the piston pin. Both the bearing and the piston pin areincluded with their masses completely in the oscillating mass of thedriving mechanism. A reduction in their masses contributes to areduction in the oscillating masses and thus allows adjustment thereof.The connecting rod is likewise included completely in the oscillatingmass in the area of the small connecting rod eye.

The bearing or the connecting rod in the area of the small connectingrod eye is then used for fine-tuning according to the invention.

Connecting rod/bearing combinations are preferable in which the materialis removed from the bearing. This gets round the removal of connectingrod material, such that there is no risk of excessively reducing thestrength of the connecting rod in the area of the small connecting rodeye. This is important, given the fact that the connecting rod supportsor carries the bearing and is one of the most highly loaded componentsprecisely in the area of the small connecting rod eye. Furthermore,removal of material is more or less noticeable as a notch, depending onthe form selected.

Connecting rod/bearing combinations are also favorable, however, inwhich the material is removed from the connecting rod. The removal ofmaterial from the bearing is limited in magnitude by the generally lowweight of the bearing itself. In this way, and due to the other aspectsto be taken into account, such as bearing strength and very largelytabooed loading zones of the bearing, tight limits are set to the amountof material which may be removed. Accordingly, if a large amount ofmaterial is to be removed, it is advisable for it to be removed from theconnecting rod.

Embodiments of the connecting rod/bearing combination are preferable inwhich the connecting rod/bearing combination is post-machined in such away that it comprises at least one recess.

This connecting rod/bearing combination according to the invention isbased on the concept that a recess arranged in the area of the smallconnecting rod eye and formed by material removal leads to a reductionin the weight of the oscillating masses, so achieving tuning of theconnecting rod/piston combination. This in turn allows achievement ofthe objective of compensation of the mass forces acting on the drivingmechanism.

Embodiments of the connecting rod/bearing combination are preferable inwhich the recess, of which there is at least one, is arranged in theareas of the bearing subject to low load, wherein the material may beremoved both from the connecting rod and the bearing.

Experience shows that the areas of the bearing subject to low load liein the areas which, measured perpendicularly to the longitudinal axis ofthe connecting rod, exhibit the greatest distance from the longitudinalaxis of the connecting rod. This preferred arrangement of the at leastone recess takes account of the fact that a recess causes a greater orlesser notch effect, depending on the shape thereof, and leads to areduction in the strength of the bearing and/or the connecting rod atleast in the area immediately adjoining said recess.

Embodiments of the connecting rod/bearing combination are favorable inwhich the recess, of which there is at least one, extends in elongatemanner in the circumferential direction of the bearing.

Embodiments of the connecting rod/bearing combination are preferable inwhich the recess, of which there is at least one, is arranged centrallybetween the two end faces of the bearing, i.e. the bushing or the plainbearing coating.

A central arrangement of the recess without the recess being opentowards the end faces of the bearing allows the recess to be used as anoil reservoir.

The present invention also relates to the method of producing theconnecting rod/bearing combination according to the invention.

In the method according to the invention for producing a connectingrod/bearing combination, material is removed in such a manner that

-   -   the small connecting rod eye of the connecting rod is provided        with a bearing, in particular with a bushing or a plain bearing        coating, and this connecting rod/bearing combination is put        together with a piston, with the addition of the necessary        accessories such as piston pins and the like, to form a        connecting rod/piston combination, and    -   it is then determined how much material mass needs to be removed        from the connecting rod/bearing combination to achieve a        predetermined connecting rod/piston combination of given mass        and mass distribution, and    -   then the connecting rod/bearing combination is post-machined in        the area of the small connecting rod eye in such a manner that        material is removed to the extent of the determined mass.

The post-machining performed is conformed to each specific individualcase, such that the depth and size of the recess may vary as a functionof the determined mass and mass distribution of the respectiveconnecting rod/piston combination.

The material is removed from the connecting rod or from the bearing orfrom the connecting rod and the bearing.

Embodiments of the method are advantageous in which post-machining isperformed, in the case of a bushing, on the bushing mounted in the smallconnecting rod eye. This makes it unnecessary to remove the bushing fromthe small connecting rod eye again for the purpose of post-machining.Consequently, the total number of method steps is reduced, therebyreducing production costs. In addition, removing the bushing again wouldlead to inaccuracies, since identical re-insertion is impossible.

Methods are advantageous in which post-machining of the connectingrod/bearing combination is performed in such a way that at least onerecess is formed.

Methods are favorable in which material is removed by milling to formthe recess, of which there is at least one.

Embodiments of the method are preferable in which material is removed byvibratory grinding to form the recess, of which there is at least one.

Methods are preferable in which material is removed by laser to form therecess, of which there is at least one.

In methods of producing a connecting rod/bearing combination with amultilayer bearing, which comprises at least one backing layer and oneoverlay, embodiments of the method are advantageous in which thematerial is removed from the bearing overlay.

The overlay forms the inner contour of the bearing and is thus thesurface of the bearing facing the piston pin and on which the lubricantfilm forms. By removing material from the bearing overlay, the strengthof the bearing, which is derived substantially from the backing layer,is reduced only slightly. In addition, the possibility is opened up ofusing a recess formed in the overlay by material removal as a reservoirfor the lubricant used.

The invention will be explained in more detail with reference to anexemplary embodiment according to the following drawings, in which:

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic representation, in side view, of a drivingmechanism of an internal combustion engine, and

FIG. 2 is a schematic representation, in side view, of an equivalentsystem for the driving mechanism shown in FIG. 1, and

FIG. 3 is a side view of a connecting rod, viewed in the direction ofthe connecting rod eye axis, and

FIG. 4 is a side view of a connecting rod, viewed in the directionperpendicular to the connecting rod eye axis and in section.

FIGS. 1 and 2 have already been explained.

DETAILED DESCRIPTION OF THE INVENTION

The connecting rod 5 shown in FIG. 3 is illustrated in side view,wherein it is observed in the direction of the connecting rod eye axis.It comprises a small connecting rod eye 6, which is always of closedconstruction and is connected to the connecting rod head 10 via theconnecting rod shank 7. The connecting rod head 10 is of splitconstruction for the purpose of mounting the connecting rod 5 on thecrankshaft. The connecting rod 5 shown in FIG. 3 has a transverselysplit connecting rod head 10, which consists of the foot 8 of theconnecting rod and the connecting rod cap 9.

The bearing 1, which may be a bushing or a plain bearing coating, isarranged in the small connecting rod eye 6. This bearing 1 serves inturn to accommodate a piston pin, not shown. The plain bearing bushing 1illustrated in FIG. 3 is a one-piece bushing 1. FIG. 3 shows an end face4 of the connecting rod 5, while the recess arranged in the bushing 1 isnot visible in side view.

To this end, the connecting rod 5 is shown in section in FIG. 4, saidsection being taken along the longitudinal axis of the connecting rodand containing the connecting rod eye axis.

The plain bearing bushing 1 with its outward facing end faces 3, 4 isillustrated in the installed state, i.e. incorporated into the smallconnecting rod eye 6. The embodiment of the plain bearing bushing 1illustrated in FIG. 4 comprises a recess 2. This recess is located in anarea of the bushing 1 subject to low load and extends in elongate mannerin the circumferential direction of the bushing 1. It is arrangedcentrally between the two end faces 3, 4 of the bushing 1 and may thusalso serve as an oil reservoir.

LIST OF REFERENCE NUMERALS

-   1 Bearing-   2 Recess-   3 End face-   4 End face-   5 Connecting rod-   6 Small connecting rod eye-   7 Connecting rod shank-   8 Connecting rod saddle-   9 Connecting rod cap-   10 Connecting rod head-   20 Driving mechanism-   21 Piston-   22 Connecting rod-   23 Cranked portion of shaft-   24 Oscillating equivalent mass m_(h)-   25 Rotating equivalent mass m_(r)-   26 Counterweight

1. A method of producing a connecting rod/bearing combination having abearing for a small connecting rod eye of a connecting rod, which servesto accommodate a piston pin mounting a piston, wherein the connectingrod/bearing combination is post-machined in the area of the smallconnecting rod in such a way that material is removed of a mass whichcorresponds to the difference between the oscillating mass of theconnecting rod/piston combination and a predetermined oscillating mass,wherein the material is removed in such a way that: the small connectingrod eye of the connecting rod is provided wit a bearing selected from agroup consisting of a bushing and a plain bearing layer to form aconnecting rod/bearing combination, and this connecting rod/bearingcombination is put together with a piston and a piston pin to form aconnecting rod/bearing/piston combination, and it is then determined howmuch material mass needs to be removed from the connectingrod/bearing/piston combination to achieve a predetermined connectingrod/bearing/piston combination of given mass and mass distribution, andthen the connecting rod/bearing combination is post-machined in the areaof the small connecting rod eye in such a manner that material isremoved to the extend of the determined mass.
 2. The method of producinga connecting rod/bearing combination as claimed in claim 1, wherein thematerial is removed from the bearing.
 3. The method of producing aconnecting rod/bearing combination as claimed in claim 1, wherein thematerial is removed from the connecting rod.
 4. The method of producinga connecting rod/bearing combination as claimed in claim 1 wherein thematerial is removed from the connecting rod and the bearing.
 5. Themethod of producing a connecting rod/bearing combination as claimed inclaim 1 wherein post-machining of the connecting rod/bearing combinationis performed in such a way that at lest one recess is formed.
 6. Themethod of producing a connecting rod/bearing combination as claimed inclaim 5, wherein material is removed by milling to form the recess, ofwhich there is at least one.
 7. The method of producing a connectingrod/bearing combination as claimed in claim 5, wherein material isremoved by vibratory grinding to form the recess, of which there is atleast one.
 8. The method of producing a connecting rod/bearingcombination as claimed in claim 5, wherein material is removed by laserto form the recess, of which there is at least one.
 9. The method forproducing a connecting rod/bearing combination as claimed in claim 1,wherein the bearing is a multilayer bearing, which comprises at leastone backing layer and one overlay, and wherein material is removed formthe overlay of the bearing.